Dissociation of leukocyte alkaline phosphatase from the bactericidal activity of neutrophils

Abstract

We have identified an apparently healthy individual with no history of repeated infections whose neutrophils were virtually devoid ofalkaline phosphatase activity by either spectrophotometric or histochemical assay. His cells showed normal bactericidal activity toward both Staphylococcus aureus and Escherichia coli when tested in vitro. We have also demonstrated that L-p-bromolevamisole, a potent inhibitor of alkaline phosphatase in many tissues, is likewise an effective inhibitor of the neutrophilic enzyme. Concentrations of this compound which caused nearly complete inhibition of the neutrophilic enzyme did not impair the ability of intact cells to kill bacteria. These results suggest that leukocyte alkaline phosphatase is not required for the normal bactericidal activity of neutrophils.The enzyme alkaline phosphatase (orthophosphoric monoester phosphohydrolase, EC 3.1.3.1) is very nearly ubiquitous, yet its function remains obscure (4). There is some suggestion in the literature that the enzyme in human polymorphonuclear leukocytes is involved in the normal bactericidal activity of the cell. Strauss et al. (15) reported a patient with absent neutrophil alkaline phosphatase activity and a purported granule abnornality; the patient was subject to recurrent bacterial infections, and his cells demonstrated a slight impairment in bactericidal activity when tested in vitro. Similarly, Repine et al. (14) reported a patient with repeated infections associated with a primary deficiency in leukocyte alkaline phosphatase (LAP). Again, a marginal defect in in vitro bactericidal activity was reported. Finally, patients with infantile hypophosphatasia and a complete absence of LAP have been reported to suffer from severe bacterial infections (5); in vitro studies of leukocyte function, however, have not been performed on such patients to the best of our knowledge.In the present paper, we describe an apparently healthy individual with markedly abnormal LAP and normal bactericidal activity of his cells. We utilized a specific chemical inhibitor of LAP, L-p-bromolevamisole, and demonstrated a marked inhibition of the enzyme derived from normal cells with no effect on the bactericidal activity of the intact cells. These results suggest there is no necessary correlation between leukocytic function and the activity of LAP.MATERIALS AND METHODS Isolation of leukocytes. Leukocytes were isolated from normal human volunteers and from an individual with markedly decreased LAP. This patient, a white 30-year-old male with no past history of bacterial infection, remained completely asymptomatic over a 3-year period of study. His peripheral smear was normal upon repeated examination; he consistently maintained a normal absolute leukocyte count with a normal differential. The finding of reduced alkaline phosphatase activity was an incidental observation when he volunteered to serve as a source of control cells in an experiment; it was subsequently verified on numerous occasions by both biochemical and histochemical techniques. The patient ...